1. Field of the Invention
This invention relates generally to containers, and particularly to containers of the type having an easy-open end that is openable by a pull-tab mechanism.
2. Description of the Related Technology
The term xe2x80x9ceasy open endxe2x80x9d is used generally for that class of ends for containers which are provided with a mechanism for permitting the consumer to open the container at the end for access to the ingredients within the container, without the use of a can opener or other machinery. One conventional easy open end technique employs a pull tab having a pointed nose, the pull tab being riveted to the panel of the end so that the nose rests adjacent a weakened area along the periphery of the end panel. To open, the pull tab is rotated about the rivet, causing the nose to fracture the weakened area. Further pulling of the tab away from the end panel then causes the remainder of the weakened peripheral to rupture, thereby permitting the entire end to be opened.
One form of easy-open end that is in wide use is the so called xe2x80x9cfull-openxe2x80x9d end, in which a peripheral score, generally circular in configuration, is formed in the end panel at or adjacent to the periphery thereof to permit its complete removal. Full-open type cans are to be distinguished from those self opening cans which have a comparatively small removable section which, when opened, provide a comparatively small hole for dispensing the product. The latter type of can end is only appropriate for packaging soda, beer, or other liquids. Full-open type cans, on the other hand, are suitable for packaging solid products such as candy, nuts, meats, or ground coffee.
One disadvantage of easy-open ends that is generally recognized by everyone who is involved in the field relates to the sharp edges that result after the can end is opened and the consequential safety issues. U.S. Pat. No. 4,511,299 to Zysset addresses these issues, and is notable in that it provided the concept of using blunt, protective shoulders formed by folding the panel end wall near the line of weakness. The method that is disclosed in the Zysset patent is depicted in FIGS. 1 through 6. As may be seen in FIG. 1, the starting material is a planar can end blank 10. The end blank 10 is first subjected to a first bending step to form bend 16 and a portion of a side curl 18 at the peripheral edge of the end 10. As shown in FIG. 2, the end is then subjected to another bending and forming step to create a pair of concentric grooves 20, 22 which define inner and outer beads 21, 23 that extend below the second, inner surface 14 of the end 10. Also formed is a central bead 24, which extends above the level of the first, outer surface 12 of the end 10. As is shown in FIG. 2, the groove 20 (and as a consequence the bead 21) extends a greater distance below the level of the second surface 14 than the outer bead 23. This dimensional characteristic is provided to insure sufficient metal on the inside of the tear area as opposed to the outside area.
Referring now to FIG. 3, the end 10 is subjected to another forming step wherein the portion of the end 10 inside the bead 21 is rolled upward, and the second bead 23 is extended downwardly. Thereafter, as is shown in FIG. 4, a score 28 is formed on the central bead 24, and then the inner and outer beads 21, 23 are forced toward the inside surface 14 and the central bead 24 is forced toward the outside surface 12 until the inner and outer beads 21, 23 abut the central bead 24 to provide blunt, protective shoulders underneath the score line 28 (see FIG. 5). The protective shoulders formed by the inner and outer beads 21, 23 lie in a common plane which is substantially parallel to, but spaced from the plane of the end 10. As is shown in FIG. 6, the completed end is provided with a pull-tab 34, the extremity of which extends adjacent to the score line 28 to permit the end to be opened in a conventional manner. As may be seen in FIGS. 6 and 7, a completed end fabricated in accordance with the method shown in FIGS. 1-5 includes the central bead 24 that contains the score line which is flush with the end 10 and resides essentially in the plane of the end 10, and concentric recesses 30, 32 that surround the central bead. The recesses 30, 32 are formed by the specific bending technique described below with respect to the inner and outer beads 21, 23.
In all types of easy open ends, including that which is described above, it is important to tightly control the manufacturing tolerances of what is termed the residual, which is the thickness of material remaining after the score has been made in the end panel. The residual is of course affected by the original thickness of the end panel in the area at which the score is been made, as well as the specific tooling and procedure by which the scoring process is accomplished. In the process that is described above and in the Zysset patent, the bending of the end panel of the end blank of course changes the thickness of the end panel in different locations, including the central bead area 24 in which the score 28 is to be placed. In general, the creation of the shoulders on each side of the location at which the score 28 is to be placed will tend to thicken this central a bead 24, which, when the scoring is performed with standard tooling, will have the effect of increasing the residual to an unwanted and unpredictable extent.
In addition, the step of compressing the beads 21, 23, 24 that occurs between FIGS. 4 and 5 will have the effect of causing material to migrate out of the shoulder areas into adjacent areas, where it is unwanted. The resulting excess material represents an added cost to the container manufacturer which is generally to be avoided.
A need exists for an improved easy-open end and a process for making such an end that is capable of controlling the score residual to a greater tolerance, and that is also further more material efficient than the process that is described above.
It is an object of the invention to provide an improved easy-open end a process for making such an end that is capable of controlling the score residual to a greater tolerance than the process that is described above, and that is also further more material efficient than the process that is described above.
In order to achieve the above and other aspects of the invention, a method of making an easy-open end for a container includes steps of providing a can end having a peripheral edge and a panel that has opposing first and second sides with the first side adapted to face toward the inside of a container when the end is affixed thereto; forming first and second grooves in the panel spaced from the peripheral edge, the grooves extending below the level of the first side to form inner and outer beads; forming a central bead in the panel between the first and second grooves, the central bead extending above the level of the second surface; forming a score along the central bead by simultaneously forming the score and compressing the central bead, whereby the depth of the score and the thickness of the central bead are both positively controlled; forcing the inner and outer beads toward each other and then toward the first surface and the central bead toward the second surface until the inner and outer beads abut the central bead; and fixing a pull-tab to the end, the pull-tab having means for severing the end along the score.
According to a second aspect of the invention, a method for forming a container having a pull-tab removable end includes steps of providing a metallic can end; forming inner and outer concentric beads in the end extending away from the end, the inner bead extending a greater distance away from the end than the outer bead; forming a score between the inner and outer beads by simultaneously forming the score and compressing the central bead, whereby the depth of the score and the thickness of the central bead are both positively controlled; forcing the inner and outer beads toward each other and toward the plane of the end until the beads abut the end; and fixing a pull-tab to the end, the pull-tab having means for severing the end along the score.